Method of treating a lumenal bifurcation

ABSTRACT

A prosthesis is disclosed for placement at an Os opening from a main body lumen to a branch body lumen. The prosthesis comprises a radially expansible support at one end, a circumferentially extending link at the other end and at least one frond extending axially therebetween. The support is configured to be deployed in the branch body lumen, with the circumferentially extending link in the main lumen and the frond extendable across the Os.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a Continuation-In-Part of U.S. patent applicationSer. No. 11/076,448 filed on Mar. 9, 2005 now U.S. Pat. No. 7,731,747,which is a Continuation-in-Part of U.S. patent application Ser. No.10/807,643 filed on Mar. 23, 2004 now U.S. Pat. No. 7,481,834, whichclaims the benefit of priority of U.S. Provisional Application No.60/463,075, filed on Apr. 14, 2003, the full disclosures of which areincorporated in their entireties herein by reference. This applicationalso is a continuation-in-part of U.S. patent application Ser. No.10/965,230, filed on Oct. 13, 2004, and the full disclosure of which isincorporated by reference in its entirety herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Embodiments of the present invention relate generally to medical devicesand methods. More particularly, embodiments of the present inventionrelate to the structure and deployment of a prosthesis having a stent orother support structure and at least one, and in some implementations atleast two fronds for deployment at a branching point in the vasculatureor elsewhere.

Maintaining the patency of body lumens is of interest in the treatmentof a variety of diseases. Of particular interest to the presentinvention are the transluminal approaches to the treatment of bodylumens. More particularly, the percutaneous treatment of atheroscleroticdisease involving the coronary and peripheral arterial systems.Currently, percutaneous coronary interventions (PCI) often involve acombination of balloon dilation of a coronary stenosis (i.e. a narrowingor blockage of the artery) followed by the placement of an endovascularprosthesis commonly referred to as a stent.

A major limitation of PCI/stent procedures is restenosis, i.e., there-narrowing of a blockage after successful intervention typicallyoccurring in the initial three to six months post treatment. The recentintroduction of drug eluting stents (DES) has dramatically reduced theincidence of restenosis in coronary vascular applications and offerspromise in peripheral stents, venous grafts, arterial and prostheticgrafts, as well as A-V fistulae. In addition to vascular applications,stents are being employed in treatment of other body lumens includingthe gastrointestinal systems (esophagus, large and small intestines,biliary system and pancreatic ducts) and the genital-urinary system(ureter, urethra, fallopian tubes, vas deferens).

Treatment of lesions in and around branch points generally referred toas bifurcated vessels, is a developing area for stent applications,particularly, since at least about 5%-10% of all coronary lesionsinvolve bifurcations. However, while quite successful in treatingarterial blockages and other conditions, current stent designs arechallenged when used at a bifurcation in the blood vessel or other bodylumen. Presently, many different strategies are employed to treatbifurcation lesions with currently available stents all of which havemajor limitations.

One common approach is to place a conventional stent in the main orlarger body lumen over the origin of the side branch. After removal ofthe stent delivery balloon, a second wire is introduced through a cellin the wall of the deployed stent and into the side branch. A balloon isthen introduced into the side branch and inflated to enlarge theside-cell of the main vessel stent. This approach can work well when theside branch is relatively free of disease, although it is associatedwith increased rates of abrupt closure due to plaque shift anddissection as well as increased rates of late restenosis.

Another commonly employed strategy is the ‘kissing balloon’ technique inwhich separate balloons are positioned in the main and side branchvessels and simultaneously inflated to deliver separate stentssimultaneously. This technique is thought to prevent plaque shift.

Other two-stent approaches including Culotte, T-Stent and Crush Stenttechniques have been employed as well. When employing a T-Stentapproach, the operator deploys a stent in the side branch followed byplacement of a main vessel stent. This approach is limited by anatomicvariation (angle between main and side branch) and inaccuracy in stentpositioning, which together can cause inadequate stent coverage of theside branch origin commonly referred to as the ostium or Os. Morerecently, the Crush approach has been introduced in which theside-vessel stent is deployed across the Os with portions in both themain and side branch vessels. The main vessel stent is then deliveredacross the origin of the side branch and deployed, which results incrushing a portion of the side branch stent between the main vesselstent and the wall of the main vessel. Following main-vessel stentdeployment, it is difficult and frequently not possible to re-enter theside branch after crush stenting. Unproven long-term results coupledwith concern regarding the inability to re-enter the side branch,malaposition of the stents against the arterial wall and the impact ofthree layers of stent (which may be drug eluting) opposed against themain vessel wall has limited the adoption of this approach.

These limitations have led to the development of stents specificallydesigned to treat bifurcated lesions. One approach employs a stentdesign with a side opening for the branch vessel which is mounted on aspecialized balloon delivery system. The specialized balloon deliverysystem accommodates wires for both the main and side branch vessels. Thesystem is tracked over both wires which provides a means to axially andradially align the stent/stent delivery system. The specialized mainvessel stent is then deployed and the stent delivery system removedwhile maintaining wire position in both the main and side branchvessels. The side branch is then addressed using the kissing balloontechnique or by delivering an additional stent to the side branch.Though this approach has many theoretical advantages, it is limited bydifficulties in tracking the delivery system over two wires (See, e.g.,U.S. Pat. Nos. 6,325,826 and 6,210,429 to Vardi et al.).

Notwithstanding the foregoing efforts, there remains a need for improveddevices as well as systems and methods for delivering devices, to treatbody lumens at or near the location of an Os between a main body lumenand a side branch lumen, typically in the vasculature, and moreparticularly in the arterial vasculature. It would be further desirableif such systems and methods could achieve both sufficient radial supportas well as adequate surface area coverage in the region of the Os andthat the prostheses in the side branches be well-anchored at or near theOs.

2. Description of the Related Art

Stent structures intended for treating bifurcated lesions are describedin U.S. Pat. Nos. 6,599,316; 6,596,020; 6,325,826; and 6,210,429. Otherstents and prostheses of interest are described in the following U.S.Pat. Nos. 4,994,071; 5,102,417; 5,342,387; 5,507,769; 5,575,817;5,607,444; 5,609,627; 5,613,980; 5,669,924; 5,669,932; 5,720,735;5,741,325; 5,749,825; 5,755,734; 5,755,735; 5,824,052; 5,827,320;5,855,598; 5,860,998; 5,868,777; 5,893,887; 5,897,588; 5,906,640;5,906,641; 5,967,971; 6,017,363; 6,033,434; 6,033,435; 6,048,361;6,051,020; 6,056,775; 6,090,133; 6,096,073; 6,099,497; 6,099,560;6,129,738; 6,165,195; 6,221,080; 6,221,098; 6,254,593; 6,258,116;6,264,682; 6,346,089; 6,361,544; 6,383,213; 6,387,120; 6,409,750;6,428,567; 6,436,104; 6,436,134; 6,440,165; 6,482,211; 6,508,836;6,579,312; and 6,582,394.

SUMMARY OF THE INVENTION

There is provided in accordance with one aspect of the presentinvention, a prosthesis for placement at an ostium or Os opening from amain body lumen to a branch body lumen. The prosthesis comprises aradially expansible branch vessel support, configured to be deployed inat least a portion of the branch body lumen. At least one, and in someimplementations a plurality of fronds extend axially from the support. Aradially expansible connector, spaced axially apart from the branchvessel support is provided for connecting at least two points on thefrond, and optionally at least two or all of the fronds in a multi frondimplementation of the invention.

In accordance with a further aspect of the present invention, there isprovided a method for treating a bifurcation between a main lumen and abranch lumen. The method comprises the steps of providing a radiallyexpandable scaffold, having a proximal end, a distal end, a supportstructure on the distal end, a circumferential link on the proximal endand at least two fronds extending axially between the support structureand the circumferential link. The scaffold is transluminally navigatedto a treatment site, and deployed at the site such that the support isin the branch lumen and the circumferential link is in the main lumen.

The method may additionally comprise a step of positioning an inflatableballoon in the main lumen, and deforming the circumferential link suchthat it conforms to at least a portion of the wall of the main lumen.The method may additionally comprise the step of deploying a stent inthe main lumen, to trap fronds between the main vessel stent and theadjacent vessel wall.

In accordance with a further aspect of the present invention, there isprovided a prosthesis for placement at an opening from a main body lumento a branch body lumen. The prosthesis comprises a radially expansiblesupport, the support configured to be deployed in at least a portion ofthe branch body lumen. A plurality of fronds extend axially from thesupport, and at least one circumferential link connects at least a firstand a second frond, the circumferential link spaced axially apart fromthe support. Preferably, the circumferential link connects each of theplurality of fronds. At least a portion of the prosthesis may beprovided with a drug coating. The drug coating may be a drug elutingcoating, and may be configured to exhibit at least one of a controlleddrug release rate, a constant release rate, bi-modal drug release rate,or a controlled concentration of drug proximate a target vessel wall.

Further features and advantages of the present invention will becomeapparent from the detailed description of preferred embodiments whichfollows, when considered together with the attached drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a prosthesis constructed inaccordance with the principles of the present invention.

FIG. 1A is a detailed view of the fronds of the prosthesis of FIG. 1,shown with the fronds deployed in broken line.

FIG. 2 is a cross-sectional view taken along line 2-2 of FIG. 1.

FIGS. 2A-2E are lateral views showing embodiments of a stent havingfronds in a rolled out configuration. FIG. 2A shows an embodiment havingserpentine-shaped fronds, FIG. 2B shows an embodiment having filamentshaped fronds, while FIG. 2C shows an embodiment having filament shapedfronds with alternating shortened fronds. FIGS. 2D and 2E illustrate anested transition zone configuration with two different stent wallpatterns.

FIG. 2F is a lateral view as in FIG. 2D, with the added feature of acircumferential link to assist in maintaining the spacial orientation ofthe fronds.

FIGS. 3A and 3B are lateral and cross sectional views illustrating anembodiment of a stent having fronds and an underlying deployment balloonhaving a fold configuration such that the balloon folds protrude throughthe spaces between the fronds.

FIGS. 4A and 4B are lateral and cross sectional views illustrating theembodiment of FIGS. 3A and 3B with the balloon folded over to capturethe fronds.

FIGS. 5A-5C are lateral views illustrating the deployment of stentfronds using an underlying deployment balloon and a retaining cuffpositioned over the proximal portion of the balloon. FIG. 5A showspre-deployment, the balloon un-inflated; FIG. 5B shows deployment, withthe balloon inflated; and FIG. 5C post-deployment, the balloon nowdeflated.

FIGS. 6A-6B are lateral views illustrating the change in shape of thecuff during deployment of a stent with fronds. FIG. 6A shows the balloonin an unexpanded state; and FIG. 6B shows the balloon in an expandedstate, with the cuff expanded radially and shrunken axially.

FIGS. 6C-6D are lateral views illustrating an embodiment of a cuffconfigured to evert upon balloon inflation to release the fronds.

FIGS. 7A-7B are lateral views illustrating an embodiment of a tether forrestraining the stent fronds.

FIGS. 8A-8B are lateral views illustrating an embodiment of a proximallyretractable sleeve for restraining the stent fronds.

FIGS. 9A-9B, 10A-10B and 11A-11B illustrate deployment of a stent at anOs between a main blood vessel and a side branch blood vessel inaccordance with the principles of the methods of the present invention.

FIGS. 12A-12H are lateral and cross section views illustratingdeployment of a stent having filament fronds an Os between a main bloodvessel and a side branch blood vessel in accordance with the principlesof the methods of the present invention.

FIGS. 13A-13C illustrate side wall patterns for three main vessel stentsuseful in combination with the prosthesis of the present invention.

FIG. 13D is an image of a deployed main vessel stent having a side wallopening in alignment with a branch vessel.

FIGS. 14A-14E are a sequence of schematic illustrations showing thedeployment of a vascular bifurcation prosthesis with linked fronds.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Embodiments of the present invention provide improved prostheses anddelivery systems for their placement within a body lumen, particularlywithin a bifurcated body lumen and more particularly at an Os openingfrom a main body lumen to a branch body lumen. The prostheses anddelivery systems will be principally useful in the vasculature, mosttypically the arterial vasculature, including the coronary, carotid andperipheral vasculature; vascular grafts including arterial, venous, andprosthetic grafts such as a bifurcated abdominal aortic aneurysm graft,and A-V fistulae. In addition to vascular applications, embodiments ofthe present invention can also be configured to be used in the treatmentof other body lumens including those in the gastrointestinal systems(e.g., esophagus, large and small intestines, biliary system andpancreatic ducts) and the genital-urinary system (e.g., ureter, urethra,fallopian tubes, vas deferens), and the like.

The prosthesis in accordance with the present invention generallycomprises three basic components: a stent or other support, at least onefrond extending from the support, and a transition zone between thesupport and the frond. These components may be integrally formed such asby molding, or by laser or other cutting from tubular stock, or may beseparately formed and secured together.

The term “fronds” as used herein will refer to any of a variety ofstructures including anchors, filaments, petals or other independentlymultiaxially deflectable elements extending from the stent or othersupport structure, to engage an adjacent main vessel stent or otherassociated structure. These fronds can expandably conform to and atleast partially circumscribe the wall of the main body vessel toselectively and stably position the prosthesis within the side branchlumen and/or optimize wall coverage in the vicinity of the ostium.Further description of exemplary frond structures and prostheses isfound in co-pending application Ser. No. 10/807,643, the full disclosureof which has previously been incorporated herein by reference. Variousembodiments of the present invention provide means for capturing orotherwise radially constraining the fronds during advancement of theprosthesis through the vasculature (or other body lumen) to a targetsite and then releasing the fronds at the desired deployment site.

The prostheses of the present invention are particularly advantageoussince they permit substantially complete coverage of the wall of thebranch body lumen up to and including the lumen ostium or Os.Additionally, the prostheses have integrated fronds which expandablyconform to and at least partially circumscribe the wall of the main bodyvessel to selectively and stably link the prosthesis to the main vesselstent. The fronds may be fully expanded to open the luminal passagethrough the main branch lumen. Such complete opening is an advantagesince it provides patency through the main branch lumen. Moreover, theopen main vessel lumen permits optional placement of a second prosthesiswithin the main branch lumen using conventional techniques.

In a first aspect of the present invention, a prosthesis comprises aradially expansible support and at least one or often two or more frondsextending axially from an end of the support. The fronds are adapted toextend around, or “expandably circumscribe” a portion of, usually atleast one-half of the circumference of the main vessel wall at or nearthe Os when the support is implanted in the branch lumen with the frondsextending into the main lumen. By “expandably circumscribe,” it is meantthat the fronds will extend into the main body lumen after initialplacement of the support within the branch body lumen. The fronds willbe adapted to then be partially or fully radially expanded, typically byexpansion of a balloon or other expandable structure therein, so thatthe fronds deform outwardly and conform to the interior surface of themain lumen.

The fronds will usually extend axially within the main vessel lumen forsome distance after complete deployment. In certain embodiments, thecontact between the fronds and the main vessel wall will usually extendboth circumferentially (typically at least one frond may cover an arcequal to one-half or more of the circumference of the main vessel) andaxially.

Deformation of the fronds to conform to at least a portion of the wallof the main body lumen provides a generally continuous coverage of theOs from the side branch lumen to the main vessel lumen. Further and/orcomplete expansion of the fronds within the main body lumen may pressthe fronds firmly against the main body lumen wall and open up thefronds so that they do not obstruct flow through the main body lumen,while maintaining patency and coverage of the side branch and os.

Usually, the prosthesis will include at least two or three frondsextending axially from the end of the support. The prosthesis couldinclude four, five, or even a greater number of fronds, but the use ofthree such fronds is presently contemplated for a coronary arteryembodiment. The fronds will have an initial length (i.e., prior toradial expansion of the prosthesis) which is at least about 1.5 timesthe width of the prosthesis prior to expansion, typically at least about2 times the width, more typically at least about 5 times the width, andoften about 7 times the width or greater. The lengths will typically beat least about 2 mm, preferably at least about 3 mm, and more preferablyat least about 6 mm. The frond length may also be considered relative tothe diameter of the corresponding main vessel. For example, a prosthesisconfigured for use in a branch vessel from a main vessel having a 3 mmlumen will preferably have a frond length of at least about 7 mm and insome embodiments at least about 9 mm.

Embodiments of the present invention incorporating only a single frondare also contemplated. The single frond may extend axially from thebranch vessel support as has been described in connection with multifrond embodiments. Alternatively, the single frond (or two or three ormore fronds) may extend in a helical or spiral pattern, such that itwraps in a helical winding about the longitudinal axis extending throughthe branch vessel support.

The fronds may have a fixed width or a width which is expandable toaccommodate the expansion of the support, and the fronds may be “hinged”at their point of connection to the support to permit freedom to adaptto the geometry of the main vessel lumen as the prosthesis is expanded.As used herein, “hinged” does not refer to a specific structure such asa conventional hinge, but rather to any combination of structures,materials and dimensions that permit multiaxial flexibility of the frondrelative to the support so that the frond can bend in any directionand/or rotate about any axis to conform to the ablumenal surface of theexpanded main vessel stent under normal use conditions. It is alsopossible that the fronds could be attached at a single point to thesupport, thus reducing the need for such expandability. The fronds maybe congruent, i.e., have identical geometries and dimensions, or mayhave different geometries and/or dimensions. In particular, in someinstances, it may be desirable to provide fronds having differentlengths and/or different widths.

In another aspect of the invention, at least one of the of fronds has aloop or filament shape and includes a first expandable strut configuredto be positioned at the Os in an expanded state and provide radialsupport to an interior portion of the main body lumen. The fronds can befabricated from flexible metal wire, molded, laser cut or otherwiseformed from tube stock in accordance with known techniques. The strutcan be configured to be substantially triangular in the expanded state.Also, at least one of the fronds may be configured to be expandablydeployed proximate a vessel wall by an expandable device such as anexpandable balloon catheter.

In another aspect of the invention, a prosthesis delivery systemcomprises a delivery catheter having an expandable member and aprosthesis carried over the expandable member. The prosthesis has aradially expandable support such as a tubular stent and at least twofronds extending axially from the support. The system also includes aretainer for capturing the fronds to prevent them from divaricating fromthe expandable member as the catheter is advanced through a patient'svasculature. “Divarication” as used herein means the separation orbranching of the fronds away from the delivery catheter. Variousembodiments of the capture means prevent divarication by constrainingand/or imparting sufficient hoop strength to the fronds to prevent themfrom branching from the expandable member during catheter advancement inthe vasculature.

In one embodiment, the capturing means comprises a portion of theexpandable member that is folded over the fronds where the foldsprotrude through axial gaps between adjacent fronds. In anotherembodiment, the capturing means comprises a cuff that extends over atleast a portion of the fronds to hold them during catheter advancement.The cuff can be positioned at the proximal end of the prosthesis and canbe removed by expansion of the expandable member to either plasticallyor elastically deform the cuff, break the cuff, or reduce the cuff inlength axially as the cuff expands circumferentially. The cuff is thenwithdrawn from the target vessel. In yet another embodiment, thecapturing means can comprise a tether which ties together the fronds.The tether can be configured to be detached from the fronds prior toexpansion of the expandable member. In alternative embodiments, thetether can be configured to break or release upon expansion of theexpandable member so as to release the fronds.

In an exemplary deployment protocol using the prosthesis deliverysystem, the delivery catheter is advanced to position the prosthesis ata target location in a body lumen. During advancement, at least aportion of the fronds are radially constrained to prevent divaricationof the fronds from the delivery catheter. When the target location isreached, the radial constraint is released and the prosthesis isdeployed within the lumen.

In various embodiments, the release of the fronds and expansion of theprosthesis can occur simultaneously or alternatively, the radialconstraint can be released prior to, during, or afterexpanding/deploying the prosthesis. In embodiments where the radialconstraint comprises balloon folds covering the fronds or a cuff ortether, the constraint can be released as the balloon is inflated. Inalternative embodiments using a cuff or tether, the cuff/tether can bewithdrawn from the fronds prior to expansion of the support.

Embodiments of the above protocol can be used to deploy the prosthesisacross the Os of a branch body lumen and trailing into the main bodylumen. In such applications, the prosthesis can be positioned so thatthe stent lies within the branch body and at least two fronds extendinto the main body lumen. The fronds are then circumferentially deformedto conform to at least a portion of the main vessel wall to define amain vessel passage through the fronds. At least two and preferably atleast three fronds extend into the main body lumen.

Radiopaque or other medical imaging visible markers can be placed on theprostheses and/or delivery balloon at desired locations. In particular,it may be desirable to provide radiopaque markers at or near thelocation on the prosthesis where the stent is joined to the fronds. Suchmarkers will allow a transition region of the prosthesis between thestent and the fronds to be properly located near the Os prior to stentexpansion. The radiopaque or other markers for locating the transitionregion on the prosthesis can also be positioned at a correspondinglocation on a balloon catheter or other delivery catheter. Accordingly,in one embodiment of the deployment protocol, positioning the prosthesiscan include aligning a visible marker on at least one of the prosthesis,on the radial constraint, and the delivery balloon with the Os.

In various embodiments for deploying the prosthesis, the support isexpanded with a balloon catheter expanded within the support. In someinstances, the support and the fronds may be expanded and deformed usingthe same balloon, e.g., the balloon is first used to expand the support,partially withdrawn, and then advanced transversely through the frondswhere it is expanded for a second time to deform the fronds. A balloonthe length of the support (shorter than the total prosthesis length) canbe used to expand the support, and then be proximally retracted andexpanded in the fronds. Alternatively, separate balloon catheters may beemployed for expanding the support within the side branch and fordeforming the fronds against the wall of the main body lumen.

By “expandably circumscribe,” it is meant that the fronds will extendinto the main body lumen after initial placement of the support withinthe branch body lumen. The fronds will be adapted to then be partiallyor fully radially expanded, typically by self expansion or expansion ofa balloon or other expandable element therein, so that the fronds deformoutwardly and engage the interior of the main lumen wall. The fronds mayexpand radially in parallel with the support section of the prosthesis.Then, in a second step, the fronds may be folded out of plane as themain vessel stent or balloon is deployed.

Deformation of the fronds at least partially within the main body lumenprovides a generally continuous coverage of the Os from the side bodylumen to the main body lumen. Further and/or complete expansion of thefronds within the main body lumen may press the fronds firmly againstthe main body lumen wall and open up the fronds so that they do notobstruct flow through the main body lumen.

The prosthesis may include at least one and in some embodiments at leastthree fronds extending axially from the end of the stent. The frondswill have an initial length (i.e., prior to radial expansion of thestent) which is at least about 1.5 times the width of the stent prior toexpansion, typically at least about 2 times the width, more typically atleast about 5 times the width, and often about 7 times the width orgreater. The lengths of the fronds will typically be at least about 2mm, preferably at least about 3 mm, and more preferably at least about 6mm, as discussed elsewhere herein additional detail. The fronds willusually have a width which is expandable to accommodate the expansion ofthe stent, and the fronds may be “hinged” or otherwise flexiblyconnected at their point of connection to the prosthesis to permitfreedom to adapt to the geometry of the main vessel lumen as the stentis expanded. It is also possible that the fronds could be attached tothe single point to the prosthesis, thus reducing the need for suchexpandability. Fronds may be optimized for particular bifurcation anglesand orientations, such as by making the fronds for positioning closer tothe “toe” of the bifurcation longer than the fronds for positioningcloser to the carina or “heel” of the bifurcation.

Referring now to FIGS. 1 and 2, an embodiment of a prosthesis anddelivery system 5 of the present invention for the delivery of aprosthesis to a bifurcated vessel can include a prosthesis 10 and adelivery catheter 30. Prosthesis 10 can include at least a radiallyexpansible support section 12 and a frond section 14 with one or morefronds 16. The base of the fronds resides in a transition zone,described below. In various embodiments, the frond section 14 includesat least two axially extending fronds 16, with three being illustrated.

Balloon catheters suitable for use with the prosthesis of the presentinvention are well understood in the art, and will not be described ingreat detail herein. In general, a catheter suitable for use fordeployment of the prosthesis of the present invention will comprise anelongate tubular body extending between a proximal end and a distal end.The length of the (catheter) tubular body depends upon the desiredapplication. For example, lengths in the area of from about 120 cm toabout 140 cm are typical for use in a percutaneous transluminal coronaryapplication intended for accessing the coronary arteries via the femoralartery. Other anatomic spaces including renal, iliac, femoral and otherperipheral applications may call for a different catheter shaft lengthand balloon dimensions, depending upon the vascular access site as willbe apparent to those of skill in the art.

The catheter shaft is provided with at least one central lumen, for aninflation media for inflating an inflatable balloon carried by thedistal end of the catheter shaft. In an over the wire embodiment, thecatheter shaft is additionally provided with a guidewire lumen extendingthroughout the entire length thereof. Alternatively, the prosthesis ofthe present invention may be deployed from a rapid exchange or monorailsystem, in which a proximal access port for the guidewire lumen isprovided along the side wall of the catheter shaft distally of theproximal manifold, such as within about the distal most 20 cm of thelength of the balloon catheter, or from a convertible system as is knownin the art.

The catheter shaft for most applications will be provided with anapproximately circular cross sectional configuration, having an externaldiameter within the range of from about 0.025 inches to about 0.065inches depending upon, among other things, whether the targetbifurcation is in the coronary or peripheral vasculature. Systems mayhave diameters in excess of about 0.25 inches and up to as much as about0.35 inches in certain applications. Diameters of from about 1.5 mm upto as large as about 7 mm are contemplated for coronary indications.Additional features and characteristics may be included in thedeployment catheter design, such frond retention structures discussedbelow, depending upon the desired functionality and clinical performanceas will be apparent to those of skill in the art.

The radially expansible support section 12 will typically be expandableby an expansion device such as a balloon catheter, but alternatively itcan be self expandable. The support section 12 may be formed using anyof a variety of conventional patterns and fabrication techniques as arewell-described in the prior art.

Depending upon the desired clinical result, the support section or stent12 may be provided with sufficient radial force to maintain patency of adiseased portion of the branch lumen. This may be desirable in aninstance were vascular disease is present in the branch vessel.Alternatively, the support section 12 may be simply called upon toretain the fronds in position during deployment of the primary vascularimplant. In this instance, a greater degree of flexibility is affordedfor the configuration of the wall pattern of the support section 12. Forexample, support section 12 may comprise a helical spiral, such as aNitinol or other memory metal which is deployable from an elongatedeployment lumen, but which reverts to its helical configuration withinthe branch vessel. Alternative self expandable structures may be usedsuch as a zig-zag series of struts, connected by a plurality of proximalapexes and a plurality of distal apexes and rolled into a cylindricalconfiguration. This configuration is well understood in the vasculargraft and stent arts, as a common foundation for a self expandabletubular support.

Usually, the prosthesis will include at least three fronds extendingaxially from the support. The fronds will have an initial length (i.e.,prior to radial expansion of the support) which is at least about 1.5times the cross sectional width of the support prior to expansion,typically at least about 2 times the width, more typically at leastabout 5 times the width, and often about 7 times the width or greater.The lengths of the fronds will typically be at least about 2 mm,preferably at least about 3 mm, and more preferably at least about 6 mm,depending on the diameter of the support.

In one implementation of the present invention, the prosthesis comprisesan overall length of about 19 mm, which is made up of a stent having alength of about 9.6 mm, a targeted expanded diameter of about 2.5 mm anda plurality of fronds having a length of about 9.3 mm.

The fronds will usually have a width measured in a circumferentialdirection in the transition zone which is expandable from a first,delivery width to a second, implanted width to accommodate the expansionof the support, while maintaining optimal wall coverage by the fronds.Thus, although each of the fronds may comprise a single axiallyextending ribbon or strut, fronds are preferably configured to permitexpansion in a circumferential direction at least in the transition zonewith radial expansion of the support structure. For this purpose, eachfrond may comprise a single axially extending element, but oftencomprises at least two axially extending elements 66A and 66D, andoptimally three or more axially extending elements, which can be spacedlaterally apart from each other upon radial expansion of the prosthesis,to increase in width in the circumferential direction. The increasedwidth referred to herein will differ on a given frond depending uponwhere along the length of the frond the measurement is taken. Fronds ofthe type illustrated herein will increase in width the most at the endattached to the support, and the least (or none) at the free apex end aswill be appreciated by those of skill in the art. Circumferentiallyexpanding at least the base of the frond enables optimal wall coveragein the vicinity of the ostium, following deployment of the prosthesis atthe treatment site. In addition, multiple elements results in a greatersurface area as a biological substrate or increased delivery of pharmaagents.

In the illustrated embodiments, each of the fronds 16 has an equal widthwith the other fronds 16. However, a first frond or set of fronds may beprovided with a first width (measured in a circumferential direction)and a second frond or set of fronds may be provided with a second,different width. Dissimilar width fronds may be provided, such asalternating fronds having a first width with fronds having a secondwidth.

In each of the foregoing constructions, radially symmetry may exist suchthat the rotational orientation of the prosthesis upon deployment isunimportant. This can simplify the deployment procedure for theprosthesis. Alternatively, prosthesis of the present inventionexhibiting radial asymmetry may be provided, depending upon the desiredclinical performance. For example, a first frond or set of fronds may becentered around 0° while a second frond or set of fronds is centeredaround 180° when the prosthesis is viewed in a proximal end elevationalview. This may be useful if the fronds are intended to extend aroundfirst and second opposing sides of the main vessel stent. Asymmetry inthe length of the fronds may also be accomplished, such as by providingfronds at a 0° location with a first length, and fronds at 180°0location with a second length. As will become apparent below, such as byreference to FIG. 9A, certain fronds in the deployed prosthesis willextend along an arc which aligns with the axis of the branch vessel at adistal end, and aligns with the axis of the main vessel at a proximalend. The proximal ends of fronds of equal length will be positionedaxially apart along the main vessel lumen. If it is desired that theproximal ends of any of the fronds align within the same transversecross section through the main vessel lumen, or achieve another desiredconfiguration, fronds of different axial lengths will be required aswill become apparent to those of skill in the art.

Certain additional features may be desirable in the prosthesis and/ordeployment system of the present invention, in an embodiment in whichthe rotational orientation of the prosthesis is important. For example,the catheter shaft of the deployment system preferably exhibitssufficient torque transmission that rotation of the proximal end of thecatheter by the clinician produces an approximately equal rotation atthe distal end of the catheter. The torque transmission characteristicsof the catheter shaft may be optimized using any of a variety ofstructures which are known in the art. For example, a helical windingmay be incorporated into the wall of the catheter shaft, using any of avariety of embedding techniques, or by winding a filament around aninner tube and positioning an outer tube over the winding, subsequentlyheat shrinking or otherwise fusing the tubes together. Bi-directionaltorque transmission characteristics can be optimized by providing afirst winding in a first (e.g. clockwise) direction, and also a secondwinding in a second (e.g. counter clockwise) direction. The winding maycomprise any of a variety of materials, such as metal ribbon, or apolymeric ribbon. Various tubular meshes and braids may also beincorporated into the catheter wall.

In addition, the rotational orientation of the prosthesis is preferablyobservable fluoroscopically, or using other medical imaging techniques.For this purpose, one or more markers is preferably provided on eitherthe prosthesis, the restraint or the deployment catheter, to enablevisualization of the rotational orientation.

The sum of the widths measured in the circumferential direction of thefronds 16 when the prosthesis is in either the first, transluminalnavigation configuration or the second, deployed configuration willpreferably add up to no more than one circumference of the stent portionof the prosthesis. In this manner, the width of the frond 16 s at thelevel of attachment may be maximized, but without requiring overlapespecially in the first configuration. The width of each frond 16 maygenerally increase upon deployment of the prosthesis to at least about125%, often at least about 200%, and in some instances up to about 300%or more of its initial width, at least at the distal end (base) of thefrond 16. The proximal free end of each frond 16 may not increase incircumferential width at all, with a resulting gradation of increase incircumferential width throughout the axial length from the proximal endto the distal end of the frond. While portions of the fronds may expandas described above, in alternate constructions, the fronds may have awidth that remains constant or substantially constant throughout thelength of the frond as the prosthesis is deployed.

The fronds may be “hinged” as has been described at their point ofconnection to the support to permit freedom to adapt to the geometry ofthe main vessel lumen as the prosthesis is expanded. It is also possiblethat each frond is attached at a single point to the support, thusreducing the need for such expandability at the junction between thefrond and the support. The fronds may be congruent, i.e., have identicalgeometries and dimensions, or may have different geometries and/ordimensions. Again, further description of the fronds may be found inco-pending application Ser. No 10/807,643.

Fronds 16, will usually extend axially from the support section 12, asillustrated, but in some circumstances the fronds can be configured toextend helically, spirally, in a serpentine pattern, or otherconfigurations as long as the configuration permits placement of thestent in a vessel such that the fronds extend across the Os. It isdesirable, however, that the individual fronds be radially separable sothat they can be independently, displaced, folded, bent, rotated abouttheir longitudinal axes, and otherwise positioned within the main bodylumen after the support section 12 has been expanded within the branchbody lumen. In the schematic embodiment of FIG. 1, the fronds 16 may beindependently folded out in a “petal-like” configuration, forming petals16 p, as generally shown in broken line for one of the fronds in FIGS. 1and 2.

In preferred embodiments, fronds 16 will be attached to the supportsection 12 such that they can both bend and rotate relative to an axis Athereof, as shown in broken line in FIG. 1A. Bending can occur radiallyoutwardly and rotation or twisting can occur about the axis A or aparallel to the axis A as the fronds are bent outwardly. Such freedom ofmotion can be provided by single point attachment joints as well as twopoint attachments or three or more point attachments.

Referring now to FIG. 2A, an exemplary embodiment of a prosthesis 50(shown in a “rolled out” pattern) comprises a support or stent section52 and a frond section 54. Support section 52 comprises a firstplurality of radially expansible serpentine elements 56 which extendcircumferentially to form a cylindrical ring having a plurality of openareas or cells 57 therein. The cylindrical rings formed by serpentineelements 56 are coaxially aligned along the longitudinal axis of thesupport section 52, and, in the illustrated embodiment, alternate with asecond plurality of cylindrical rings formed by radially expandableserpentine elements 58 defining a second set of smaller cells 59. Strutcoverage in the range of from about 10% to about 20%, and in someembodiments between about 16%-18% by area is contemplated. A pluralityof spaced apart, axially extending struts 61 connect adjacent rings. Theparticular pattern illustrated for this structure is well-known andchosen to be exemplary of a useful prosthesis. It will be appreciatedthat a wide variety of other conventional stent structures and patternsmay be equally useful as the support section of the prostheses of thepresent invention. See, for example, FIGS. 2B-2F.

The wall patterns can be varied widely as desired to provide additionalcoverage, transition in axial stiffness, and accommodate various sidebranch angles with respect to the main vessel long axis as well asostial geometries, i.e., diameter and shape.

The support section 52 is joined to the frond section 54 at a pluralityof points 65 along a transition line or zone 60. Individual fronds 16,comprise a circumferentially expandable wall pattern. In the embodimentillustrated in FIG. 2A, each frond comprises four curving elements 66 atthe distal end of the transition zone 60, which reduce in number tothree and then to two in the axial (proximal) direction away from thestent 52. The particular structures shown illustrate one example of away to achieve circumferential expansion of the individual fronds as theprosthesis is expanded. This is accomplished since each frond isattached to three adjacent serpentine ring apexes 63 in the proximalmost serpentine ring 56. Thus, as these serpentine rings 56 areexpanded, the circumferential distance between adjacent apexes 63 willincrease, thereby causing each frond to “widen” by expanding in acircumferential direction. It would be possible, of course, to join eachof the fronds 16 only at a single location to the prosthesis 52, thusallowing the anchors to be deployed without radial expansion. Two orfour or more points of attachment may also be used, depending upon thewall pattern and desired performance of the resulting prosthesis. Thestruts in the transition section are designed to “cup” with adjacentstruts such that the gap formed within and between fronds in theexpanded prosthesis is minimized.

The circumferentially expandable fronds are curved about thelongitudinal axis of the prosthesis and have a number of hinge regionswhich increase their conformability upon circumferential expansion by aballoon, as described hereinafter. Such conformability is desirablesince the fronds will be expanded under a wide variety of differinganatomical conditions which will result in different final geometriesfor the fronds in use. The final configuration of the fronds in the mainvessel lumen will depend on a number of factors, including length of thefronds and geometry of the vasculature and will vary greatly fromdeployment to deployment. While the fronds together will cover at leasta portion of the main vessel wall circumference, most fronds will alsobe deformed to cover an axial length component of the main vessel wallas well. Such coverage is schematically illustrated in the figuresdiscussed below.

In other embodiments, prosthesis structure 50 can include four or fiveor six or more fronds 16. Increasing the number of fronds provides anincreased number of anchor points between a branch vessel stent and amain vessel stent. This may serve to increase the mechanical linkagebetween stent 10 and another stent deployed in an adjacent vessel. Invarious embodiments, fronds 16 can be narrower (in width) thanembodiments having few fronds so as to increase the flexibility of thefronds. The increased flexibility can facilitate the bending of thefronds during stent deployment including bending from the branch bodylumen into the main body lumen.

Referring now to FIG. 2B, in various embodiments, fronds 16 can comprisethin filaments formed into loops 17. An exemplary embodiment of aprosthesis structure 50 having a plurality of filament loops 17 is shownin FIG. 2B in a rolled out pattern. In various embodiments filamentloops 17 can have at least one or two or more intra-filament connectors18, 19 which extend in a circumferential direction to connect twoadjacent filaments defining a filament loop 17. Connectors 18, 19preferably include at least one nonlinear undulation such as a “U”, “V”or “W” or “S” shape to permit radial expansion of the prosthesis in thevicinity of the fronds. (The intra-filament space may be crossed with aballoon catheter and dilated to larger diameters).

The illustrated embodiment includes a first intra-filament connector 18in the transition area 60 for each frond 16, and a second connector 19positioned proximally from the first connector 18. One or both of thefirst and second connectors 18, 19 can be configured to expand orotherwise assume a different shape when the fronds are deployed. Atleast five or ten or 20 or more connectors 18, 19 may be providedbetween any two adjacent filaments 66 depending upon the desiredclinical performance. Also connectors 18, 19 can be continuous withfrond loops 17 and have substantially the same cross sectional thicknessand/or mechanical properties. Alternatively, connectors 18, 19 can havedifferent diameters and/or mechanical properties (e.g. one or more ofincreased elasticity, elastic limit, elongation, stiffness etc.) and orbiological properties (surface finish, passivation, coatings, etc.). Inone embodiment the distal connector 18 can be stiffer than the proximalconnector 19 so as to allow more flexibility at the proximal tip of thefronds.

Connectors 18 and 19 can be further configured to perform severalfunctions. First, to act as mechanical struts to increase the stiffness(e.g. longitudinal, torsional, etc) of the filament fronds 16. Second,when the fronds are deployed, connectors 18 and 19 can be designed toassume a deployed shape which provides radial mechanical support (e.g.act as prosthesis) to the target vessel including at the OS. This isparticularly the case for first connector 18 which can be configured tounfurl in the circumferential direction and assume a semi-triangularshape in its deployed state with an expansion axis (of the connectedpoints of the triangle to fronds) substantially parallel to the radialaxis of the vessel. This configuration of connector 18 serves to provideradial mechanical support as well as coverage at the OS in particular.Connector 18 can also be configured to assume other deployed shapes aswell, such as semi-circular etc. The number and spacing and deployedshape of the connectors 18 can be configured to provide the same amountor density at the OS (e.g. number of struts per axial or radial lengthof tissue) as the stent region 52 of the prosthesis provides to the restof the vessel. In general, by varying the dimensions and number of thefilaments 66 and connectors 18 any of a variety of physical propertiescan be achieved. The connectors 18 and 19 and filaments 66 may beselected and designed to cooperate to provide maximum area coverage,and/or maximum mechanical radial force, or either objective without theother. The number of filaments can be in the range of from about 3 toabout 30, with specific embodiments of 4, 6, 10, 20 and 25.

In various embodiments, the arrangement of the filaments fronds can beconfigured to provide several functions. First, as described above theycan be configured to provide increased coverage and hence patency of theOs by having an increased number of mechanical support points in the Osand hence a more even distribution of force (e.g. radial force) on thefronds. Also, for embodiments of drug coated stents, including drugeluting stents they provide an increased amount of surface area for theelution of the drug. This in turn, serves to provide increased and/ormore constant local concentration of the selected drug at the vesselwall and/or other target site. Other pharmacokinetic benefits can beobtained as well, such as a more constant drug release rate. For stentscoated with anti-cell proliferative, anti-inflammatory and/or anti-cellmigration drugs such as Taxol (paclitaxel), Rapamycin and theirderivatives, the use of high filament type fronds serve as a means toreduce the incidence and rate of hyperplasia and restenosis. Similarresults can be obtained with other drugs known in the art for reducingrestenosis (e.g. anti-neo-plastics, anti-inflammatory drugs, etc.). Alsoin a related embodiment the filament fronds can be coated with adifferent drug and/or a different concentration of drug as the remainderof the stent. In use, such embodiment can be configured to provide oneor more of the following: i) a more constant release rate of drug; ii)bimodal release of drug; iii) multi drug therapies; and iv) titration ofdrug delivery/concentration for specific vessels and/or release rates.As disclosed in additional detail below, the drug may be incorporatedinto a biostable, biodegradeable, or bioerodable polymer matrix, and maybe optimized for long-term pharma release (prophylactic local drugdelivery).

In general, in any of the embodiments herein, the prosthesis of thepresent invention can be adapted to release an agent for prophylactic oractive treatment from all or from portions of its surface. The activeagents (therapy drug or gene) carried by the prosthesis may include anyof a variety of compounds or biological materials which provide thedesired therapy or desired modification of the local biologicalenvironment. Depending upon the clinical objective in a givenimplementation of the invention, the active agent may includeimmunosuppressant compounds, anti-thrombogenic agents, anti-canceragents, hormones, or other anti-stenosis drugs. Suitableimmunosuppressants may include ciclosporina (CsA), FK506,DSG(15-deoxyspergualin, 15-dos), MMF, rapamycin and its derivatives,CCI-779, FR 900520, FR 900523, NK86-1086, daclizumab, depsidomycin,kanglemycin-C, spergualin, prodigiosin25-c, cammunomicin, demethomycin,tetranactin, tranilast, stevastelins, myriocin, gliotoxin, FR 651814,SDZ214-104, bredinin, WS9482, and steroids. Suitable anti-thrombogenicdrugs may include anti-platelet agents (GP IIb/IIIa, thienopyridine,GPIb-IX, ASA, etc and inhibitors for the coagulation cascade (heparin,hyrudin, thrombin inhibitors, Xa inhibitors, VIIa Inhibitors, TissueFactor Inhibitors and the like). Suitable anti-cancer (antiproliferative) agents may include methotrexate, purine, pyridine, andbotanical (e.g. paclitaxel, colchicines and triptolide), epothilone,antibiotics, and antibodies. Suitable additional anti-stenosis agentsinclude batimastat, NO donor, 2-chlorodeoxyadenosine, 2-deoxycoformycin,FTY720, Myfortic, ISA (TX) 247, AGI-1096, OKT3, Medimmune, ATG, Zenapax,Simulect, DAB486-IL-2, Anti-ICAM-1, Thymoglobulin, Everolimus, Neoral,Azathioprine (AZA), Cyclophosphamide, Methotrexate, Brequinar Sodium,Leflunomide, or Mizoribine. Gene therapy formulations include Keratin 8,VEGF, and EGF, PTEN, Pro-UK, NOS, or C-myc may also be used.

Methods of preventing restenosis include inhibiting VSMC hyperplasia ormigration, promoting endothelial cell growth, or inhibiting cell matrixproliferation with the delivery of suitable compounds from theprosthesis. Radiation, systemic drug therapy and combinations of theforegoing may also be used. The desired dose delivery profiles for theforegoing are in some cases reported in the literature, or may beoptimized for use with the prosthesis of the present invention throughroutine experimentation by those of skill in the art in view of thedisclosure herein.

Binding systems (e.g., chemical binding, absorbable and non absorbablepolymeric coatings) for releasably carrying the active agent with theprosthesis are well known in the art and can be selected to cooperatewith the desired drug elution profile and other characteristics of aparticular active agent as will be appreciated by those of skill in theart.

In general, the drug(s) may be incorporated into or affixed to the stentin a number of ways and utilizing any biocompatible materials; it may beincorporated into e.g. a polymer or a polymeric matrix and sprayed ontothe outer surface of the stent. A mixture of the drug(s) and thepolymeric material may be prepared in a solvent or a mixture of solventsand applied to the surfaces of the stents also by dip-coating, brushcoating and/or dip/spin coating, the solvent (s) being allowed toevaporate to leave a film with entrapped drug(s). In the case of stentswhere the drug(s) is delivered from micropores, struts or channels, asolution of a polymer may additionally be applied as an outlayer tocontrol the drug(s) release; alternatively, the active agent may becomprised in the micropores, struts or channels and the active co-agentmay be incorporated in the outlayer, or vice versa. The active agent mayalso be affixed in an inner layer of the stent and the active co-agentin an outer layer, or vice versa. The drug(s) may also be attached by acovalent bond, e.g. esters, amides or anhydrides, to the stent surface,involving chemical derivatization. The drug(s) may also be incorporatedinto a biocompatible porous ceramic coating, e.g. a nanoporous ceramiccoating. The medical device of the invention is configured to releasethe active co-agent concurrent with or subsequent to the release of theactive agent.

Examples of polymeric materials known for this purpose includehydrophilic, hydrophobic or biocompatible biodegradable materials, e.g.polycarboxylic acids; cellulosic polymers; starch; collagen; hyaluronicacid; gelatin; lactone-based polyesters or copolyesters, e.g.polylactide; polyglycolide; polylactide-glycolide; polycaprolactone;polycaprolactone-glycolide; poly(hydroxybutyrate);poly(hydroxyvalerate); polyhydroxy(butyrate-co-valerate);polyglycolide-co-trimethylene carbonate; poly(dioxanone);polyorthoesters; polyanhydrides; polyaminoacids; polysaccharides;polyphospoeters; polyphosphoester-urethane; polycyanoacrylates;polyphosphazenes; poly(ether-ester) copolymers, e.g. PEO-PLLA, fibrin;fibrinogen; or mixtures thereof; and biocompatible non-degradingmaterials, e.g. polyurethane; polyolefins; polyesters; polyamides;polycaprolactam; polyimide; polyvinyl chloride; polyvinyl methyl ether;polyvinyl alcohol or vinyl alcohol/olefin copolymers, e.g. vinylalcohol/ethylene copolymers; polyacrylonitrile; polystyrene copolymersof vinyl monomers with olefins, e.g. styrene acrylonitrile copolymers,ethylene methyl methacrylate copolymers; polydimethylsiloxane;poly(ethylene-vinylacetate); acrylate based polymers or copolymers, e.g.polybutylmethacrylate, poly(hydroxyethyl methylmethacrylate); polyvinylpyrrolidinone; fluorinated polymers such as polytetrafluoroethylene;cellulose esters e.g. cellulose acetate, cellulose nitrate or cellulosepropionate; or mixtures thereof.

When a polymeric matrix is used, it may comprise multiple layers, e.g. abase layer in which the drug(s) is/are incorporated, e.g.ethylene-co-vinylacetate and polybutylmethacrylate, and a top coat, e.g.polybutylmethacrylate, which is drug(s)-free and acts as adiffusion-control of the drug(s). Alternatively, the active agent may becomprised in the base layer and the active co-agent may be incorporatedin the outlayer, or vice versa. Total thickness of the polymeric matrixmay be from about 1 to 20 μ or greater.

The drug(s) elutes from the polymeric material or the stent over timeand enters the surrounding tissue, e.g. up to ca. 1 month to 10 years.The local delivery according to the present invention allows for highconcentration of the drug(s) at the disease site with low concentrationof circulating compound. The amount of drug(s) used for local deliveryapplications will vary depending on the compounds used, the condition tobe treated and the desired effect. For purposes of the invention, atherapeutically effective amount will be administered; for example, thedrug delivery device or system is configured to release the active agentand/or the active co-agent at a rate of 0.001 to 200 μg/day. Bytherapeutically effective amount is intended an amount sufficient toinhibit cellular proliferation and resulting in the prevention andtreatment of the disease state. Specifically, for the prevention ortreatment of restenosis e.g. after revascularization, or antitumortreatment, local delivery may require less compound than systemicadministration. The drug(s) may elute passively, actively or underactivation, e.g. light-activation.

A possible alternative to a coated stent is a stent containing wells orreservoirs that are loaded with a drug, as discussed by Wright et al.,in “Modified Stent Useful for Delivery of Drugs Along Stent Strut,” U.S.Pat. No. 6,273,913, issued Aug. 14, 2001; and Wright et al., in “Stentwith Therapeutically Active Dosage of Rapamycin Coated Thereon,” U.S.patent publication US 2001/0027340, published Oct. 4, 2001, thedisclosures of both of which are incorporated in their entireties hereinby reference.

Wright et al. in U.S. Pat. No. 6,273,913, describes the delivery ofrapamycin from an intravascular stent and directly from microporesformed in the stent body to inhibit neointimal tissue proliferation andrestenosis. The stent, which has been modified to contain micropores, isdipped into a solution of rapamycin and an organic solvent, and thesolution is allowed to permeate into the micropores. After the solventhas been allowed to dry, a polymer layer may be applied as an outerlayer for a controlled release of the drug.

U.S. Pat. No. 5,843,172 by Yan, which is entitled “Porous MedicatedStent”, discloses a metallic stent that has a plurality of pores in themetal that are loaded with medication. The drug loaded into the pores isa first medication, and an outer layer or coating may contain a secondmedication. The porous cavities of the stent can be formed by sinteringthe stent material from metallic particles, filaments, fibers, wires orother materials such as sheets of sintered materials.

Leone et al. in U.S. Pat. No. 5,891,108 entitled “Drug Delivery Stent”describes a retrievable drug delivery stent, which is made of a hollowtubular wire. The tubular wire or tubing has holes in its body fordelivering a liquid solution or drug to a stenotic lesion. Brown et al.in “Directional Drug Delivery Stent and Method of Use,” U.S. Pat. No.6,071,305 issued Jun. 6, 2000, discloses a tube with an eccentric innerdiameter and holes or channels along the periphery that house drugs andcan deliver them preferentially to one side of the tube. Scheerder etal. in U.S. patent publication US 2002/0007209, discloses a series ofholes or perforations cut into the struts on a stent that are able tohouse therapeutic agents for local delivery.

Referring to the patent literature, Heparin, as well as otheranti-platelet or anti-thrombolytic surface coatings, have been reportedto reduce thrombosis when carried by the stent surface. Stents includingboth a heparin surface and an active agent stored inside of a coatingare disclosed, for example, in U.S. Pat. Nos. 6,231,600 and 5,288,711.

A variety of agents specifically identified as inhibiting smoothmuscle-cell proliferation, and thus inhibit restenosis, have also beenproposed for release from endovascular stents. As examples, U.S. Pat.No. 6,159,488 describes the use of a quinazolinone derivative; U.S. Pat.No. 6,171,609, describes the use of taxol, and U.S. Pat. No. 5,716,981,the use of paclitaxel, a cytotoxic agent thought to be the activeingredient in the agent taxol. The metal silver is cited in U.S. Pat.No. 5,873,904. Tranilast, a membrane stabilizing agent thought to haveanti-inflammatory properties is disclosed in U.S. Pat. No. 5,733,327.

More recently, rapamycin, an immunosuppressant reported to suppress bothsmooth muscle cell and endothelial cell growth, has been shown to haveimproved effectiveness against restenosis, when delivered from a stent.See, for example, U.S. Pat. Nos. 5,288,711 and 6,153,252. Also, in PCTPublication No. WO 97/35575, the monocyclic triene immunosuppressivecompound everolimus and related compounds have been proposed fortreating restenosis, via systemic delivery.

Use of multiple filaments per frond also provides for a more openstructure of the fronds section 54 of the prosthesis to allow for aneasier and less obstructed passage of a guide wire and/or the deploymentballoon by and/or through the fronds (e.g., during un-jailing proceduresknown in the art). Similarly, use of the flexible filaments also allowsthe main vessel to track between fronds and engage the main vesselstent. In particular, the thinner frond filaments facilitate advancementof the fronds over the circumference and/or the length of a main vesselstent during deployment of the fronds or the main vessel stent.Moreover, the filaments can be configured to be easily withdrawn andthen re-advanced again to allow for repositioning of either of thebranch vessel stent. Other means for facilitating advancement of themain vessel stent between the fronds can include tapering the frondsand/or coating the fronds with a lubricous coating such as PTFE orsilicone (this also facilitates release of the fronds from constrainingmeans described herein). Finally, by having an increased number offilaments, the mechanical support of the Os is not compromised if one ormore filaments should become pushed aside during the stent deployment.That is, the remaining filaments provide sufficient support of the Os tomaintain it patency. In these and related embodiments, it may bedesirable to have at least six loops 17 each comprising at least onefilament looped back upon itself at its proximal limit to provide atleast two elements per frond.

Various embodiments of the fronds can be configured to provide anincreased amount of mechanical linkage between the fronds and the mainvessel stent. In general, the frond design seeks to 1) track to site, 2)allow for advancement of MV Stent 3) increase frond-MV stent interactionand 4) frond MV wall interactions. Another means includes increasing thenumber of fronds to provide an increased number of anchor points betweena branch vessel stent and a main vessel stent. This in turn provides anincreased amount of mechanical linkage between the two stents such thatthey increasingly operate mechanically as one structure rather than twoafter deployment. This also serves to improve the spatial stability ofthe deployed stents within both vessels. That is, there is reducedmovement (e.g., axial or radial) or reduced possibility of movement ofone or both stents within their respective vessels. In particular, thelinkage serves to provide radial strength of the structure in theostium.

Referring now to FIG. 2C in an alternative embodiment of a prosthesis 50having filament fronds 17, one or two or more frond can be a shortenedfrond 16 s. That is a frond that is shortened in the longitudinaldirection. In the illustrated embodiment, shortened fronds 16 s and fulllength fronds 16 alternate around the circumference of the stent. Theamount of shortening can range from 10% to 99%. In a preferredembodiment, fronds 16 s are shortened by approximately slightly lessthan 50% in length from the length of un-shortened fronds 16.Embodiments having shortened fronds, reduce the likelihood of resistancewhen the main vessel stent 150 is positioned. Shortened fronds 16 s alsocan be configured to act more like point contacts on the main vesselstent 150 and should therefore be less likely to be swept towards the Osby deployment and/or misalignment of the main vessel stent anddeployment balloon. Also, use of less material in the fronds tends toproduce less displacement of the fronds even if the main vessel stent orballoon catches multiple fronds, and may produce a lower biologicalreaction (less foreign material).

FIGS. 2D and 2E illustrate an alternative side wall patterns for thetransition portion of the prosthesis of the present invention, on stentshaving two different side wall patterns. As described previously, thespecific stent or other support structure configuration may be variedconsiderably within the context of the present invention.

In each of the embodiments of FIGS. 2D and 2E, the struts 70 at thefrond root (e.g. transition zone) are provided with an interdigitatingor nesting configuration. In this configuration, as viewed in the flat,laid out view as in FIGS. 2D and 2E, a plurality of struts 70 extendacross the transition zone. A distal segment 72 of each strut 70inclines laterally in a first direction, to an apex 74, and theninclines laterally in a second direction to a point that may beapproximately axially aligned with a distal limit of the distal segment72. The extent of lateral displacement of the strut between its originand the apex 74 is greater than the distance between adjacent struts,when in the unexpanded configuration. In this manner, adjacent strutsstack up or nest within each other, each having a concavity 78 facing ina first lateral direction and a corresponding convexity 80 in a secondlateral direction. This configuration seeks to optimize vessel wallcoverage at the ostium, when the stent is expanded.

The axial length of each frond is at least about 10%, often at leastabout 20%, and in some embodiments at least about 35% or 75% or more ofthe length of the overall prosthesis. Within this length, adjacentfronds may be constructed without any lateral interconnection, tooptimize the independent flexibility. The axially extending component ofthe frond may be provided with an undulating or serpentine structure 82,which helps enable the fronds to rotate out of the plane when the mainvessel stent is deployed. Circumferential portions of the undulatingfronds structure make the frond very flexible out of the plane of thefrond for trackability. A plurality of connectors 84 are providedbetween parallel undulating filaments 86, 88 of each frond, to keep thefrond from being overly floppy and prone to undesirable deformation.Each of the fronds in the illustrated embodiment has a broad (i.e.relatively large radius) frond tip 90, to provide an atraumatic tip tominimize the risk of perforating the arterial or other vascular wall.

The interdigitating construction in the transition zone, as well as theundulating pattern of the frond sections both provides optimal coverageat the ostium, and provides additional strut length extension orelongation capabilities, which may be desirable during the implantationprocess.

It may also be desirable to vary the physical properties of thefilaments, 86, 88, or elsewhere in the prosthesis, to achieve desiredexpansion results. For example, referring to FIG. 2E, each frond 16includes a first filament 92, attached at a first attachment point 94and a second filament 96 attached at a second attachment point 98 to thestent. A third filament 100 and a fourth filament 102 are connected tothe stent at an intermediate attachment point 104. As illustrated, thetransverse width of the third and fourth filaments 100 and 102 are lessthan the transverse width of the first and second filaments 92, 96. Thethinner filaments 100, 102 provide less resistance to expansion, andhelp maintain optimal coverage in the vicinity of the ostium uponexpansion of the prosthesis.

In any of the embodiments described herein, the fronds may be consideredto have a lumenal surface at least a portion of which will be in contactwith an outside surface of the main vessel stent, and an ablumenalsurface which will be pressed into contact with the vascular wall by themain vessel stent. The lumenal and ablumenal surfaces of the fronds maybe provided with similar or dissimilar characteristics, depending uponthe desired performance. For example, as described elsewhere herein, thefrond and particularly the ablumenal surface may be provided with a drugeluting characteristic.

It may also be desirable to modify the lumenal surface of the frond, toenhance the physical interaction with the main vessel stent. For thispurpose, the lumenal surface of the frond may be provided with any of avariety of friction enhancing surface characteristics, or engagementstructures for engaging the main vessel stent. Friction enhancingsurfaces may comprise the use of polymeric coatings, or mechanicalroughening such as laser etching, chemical etching, sputtering, or otherprocesses. Alternatively, any of a variety of radially inwardlyextending hooks or barbs may be provided, for engaging the main vesselstent. Preferably, any radially inwardly extending hooks or barbs willhave an axial length in the radial direction of no greater thanapproximately the wall thickness of the main vessel stent strut, tominimize the introduction of blood flow turbulence. Although a varietyof main vessel stents are available, the inventors presently contemplatewall thicknesses for the struts of such main vessel stents to be on theorder of about 0.003 to 0.0055 inches for native coronary indications.Any of the foregoing surfaces textures or structures may also beprovided on the ablumenal surface of the main vessel stent, to cooperatewith corresponding textures or structures on the fronds, to enhance thephysical integrity of the junction between the two, and potentiallyreduce the risk for vessel perforation by fronds.

As will be described in additional detail in connection with the method,below, proper positioning of the prosthesis with respect to thebifurcation may be important. To facilitate positioning of thetransition zone relative to the carina or other anatomical feature ofthe bifurcation, the prosthesis is preferably provided with a firstradiopaque marker at a distal end of the transition zone and a secondradiopaque marker at the proximal end of the transition zone. Theproximal and distal radiopaque markers may take the form of radiopaquebands of material, or discreet markers which are attached to theprosthesis structure. This will enable centering of the transition zoneon a desired anatomical target, relative to the ostium of thebifurcation. In general, it is desirable to avoid positioning the stentor other support such that it extends into the main vessel. A singlemarker may be used to denote the placement location of the transitionzone.

Alternatively, the marker band or bands or other markers may be carriedby the deployment catheter beneath the prosthesis, and axially alignedwith, for example, the proximal and distal ends of the transition zonein addition to markers delineating the proximal and distal end of theprosthesis

Although the prosthesis has been disclosed herein primarily in thecontext of a distal branch vessel stent carrying a plurality ofproximally extending fronds, other configurations may be constructedwithin the scope of the present invention. For example, the orientationsmay be reversed such that the fronds extend in a distal direction fromthe support structure. Alternatively, a support structure such as astent may be provided at each of the proximal and distal ends of aplurality of frond like connectors. This structure may be deployed, forexample, with a distal stent in the branch lumen, a plurality ofconnectors extending across the ostium into the main vessel, and theproximal stent deployed in the main vessel proximal to the ostium. Aseparate main vessel stent may thereafter be positioned through theproximal stent of the prosthesis, across the ostium and into the mainvessel on the distal side of the bifurcation.

In addition, the prosthesis has been primarily described herein as aunitary structure, such as might be produced by laser cutting theprosthesis from a tubular stock. Alternatively, the prosthesis may beconstructed such as by welding, brazing, or other attachment techniquesto secure a plurality of fronds onto a separately constructed support.This permits the use of dissimilar materials, having a variety of hybridcharacteristics, such as a self expandable plurality of fronds connectedto a balloon expandable support. Once released from a restraint on thedeployment catheter, self expandable fronds will tend to bias radiallyoutwardly against the vascular wall; which may be desirable during theprocess of implanting the main vessel stent. Alternatively, the entirestructure can be self expandable or balloon expandable, or the supportcan be self expandable as is described elsewhere herein. In general, theproximal end of the fronds will contribute no incremental radial forceto the prosthesis. The distal end of the fronds may contribute radialforce only to the extent that it is transmitted down the frond from thesupport structure.

In each of the embodiments illustrated in FIGS. 2A-2E, the fronds havebeen illustrated as extending between a first end which is attached tothe support 52, and a second, free end. In any of the frond designsdisclosed herein, it may be desirable to provide a connection betweenthe fronds in the vicinity of the free end. The connection may beaccomplished in any of a variety of ways, such as providing a series ofinterfrond segments or connections, which, when deployed and expanded,form a circumferential ring which links the fronds. Alternatively, thecircumferential link may be frangible, such that it maintains thespatial orientation of the fronds prior to a final expansion step, butis severed or otherwise releases the fronds upon final expansion.

The provision of a circumferential link at the proximal end of thefronds may provide a variety of benefits. For example, in an embodimentintended for balloon expansion at the treatment site, thecircumferential link will assist in maintaining the crimped profile ofthe fronds on the balloon during transluminal navigation. Thecircumferential link may be configured with sufficient holding forcethat an outer sleeve such as those discussed in connection with FIGS. 5and 6 may be omitted. In addition, the provision of a circumferentiallink may provide sufficient radiopacity either by itself or by carryingseparate radiopaque markers to permit visualization of the ends of thefronds.

Once at the treatment site, the circumferential link will assist inmaintaining the spacing of the fronds and also in holding the proximalends of the fronds open to facilitate advancement of the main vesselstent therethrough. The circumferential link may additionally assist incontrolling the fronds if, during the procedure, it is determined tocrush the fronds against a wall of the vessel. The circumferential linkwill assist in maintaining the fronds against the wall while a secondarystrategy is employed.

The circumferential link may be provided by any of a variety oftechniques which will be understood to those in the stent manufacturingarts. For example, the circumferential link may be formed integrallywith the stent and fronds such as by laser cutting from tube stock.Alternatively, the circumferential link may be attached to previouslyformed fronds, using any of a variety of bonding techniques such aswelding, brazing, adhesives or others depending upon the materials ofthe fronds and circumferential link. Although it may add to the wallthickness, the circumferential link may be interlocked with or crimpedto the fronds.

The circumferential link may alternatively be a polymeric band ortubular sleeve. For example, a radially expandable tubular sleeve may bepositioned around the outside surface of the fronds, or adjacent thelumenal surface of the fronds. A polymeric circumferential link may alsobe formed such as by dipping the fronds or spraying the fronds with asuitable polymeric precursor or molten material. Polymericcircumferential links may be permanent, severable, or may bebioabsorbable or bioerodeable over time.

One embodiment of a circumferential link is illustrated schematically inFIG. 2F. In this embodiment, a circumferential link 120 is provided,which connects each adjacent pair of fronds together, to produce acircumferential link 120 which extends completely around the axis of theprosthesis. In this illustration, the circumferential link 120 thuscomprises a discrete transverse connection between each adjacent pair offronds. Thus, for example, a first segment 122 is provided between afirst and a second frond. The first segment 122 is expandable orenlargeable in a circumferential direction. A first segment 122 has afirst end 126 at the point of attachment of the first segment 122 to afirst frond, and a second end 128 at a point of attachment between thefirst segment 122 and a second frond. The arc distance or the lineardistance between the first end 126 and second end 128 measured in aplane transverse to the longitudinal axis of the prosthesis isenlargeable from a first distance for transluminal navigation, to asecond distance following expansion of the fronds within the mainvessel. To accommodate the radial expansion of the circumferential link120, the first segment 122 is provided with an undulating configurationhaving at least one and optionally 2 or three or more apex 130, as willbe understood in the art. In one embodiment, each adjacent pair offronds is connected by a transverse segment (e.g., 122, 124 etc.) andeach of the transverse segments is identical to each other transversesegments.

Although the first segment 122 and second segment 124 are eachillustrated in FIG. 2F as comprising only a single transverselyextending filament, two or three or more filaments may be providedbetween each adjacent pair of fronds, depending upon the desiredperformance. As used herein, the term “circumferential link” does notlimit the link 120 to only a single filament between adjacent fronds.For example, the circumferential link may comprise a stent or othersupport structure which is similar to the support structure 52.

In general terms, the prosthesis 50 may be considered to be a tubularstructure which comprises a plurality of axially extending fronds havinga first radially expandable structure on a first end and a secondradially expandable structure on a second end. The first radiallyexpandable structure is a support structure 52 such as a stent, as hasbeen described for positioning within the branch vessel. The secondradially expandable structure comprises the circumferential link 120.

Typically, the circumferential link 120 will provide significantly lessradial force than the first support structure 52, in view of its primaryfunction to maintain the spacing and orientation of the fronds ratherthan providing support to the vessel wall. In a typical embodiment, thesupport structure 52 will have a first radial force, the circumferentiallink 120 will have a second, lesser radial force, and the fronds willcontribute nothing or essentially nothing to the radial force of thestructure. Alternatively, the circumferential link 120 may have a radialforce which is approximately equal to the radial force of the supportstructure 52, and possibly even in excess of the radial force of thesupport structure 52, depending upon the desired clinical performance.The fronds may exhibit a radial force, which may be due mostly orentirely to the adjacent stent or circumferential link.

In an implementation of the invention intended for use in the coronaryarteries, the stent portion may have a crush resistance or radialstrength on the order of at least about 10 psi or 12 psi, and, often atleast about 14 or 15 psi. The circumferential link may have a radialforce or crush resistance of no greater than about 90%, often no greaterthan about 50%, and in some embodiments no greater than about 25% of theradial force or crush resistance of the branch vessel stent. Thus, in aprosthesis having a stent with a crush resistance of at least about 14or 15 psi, the circumferential link might have a crush resistance ofless than about 4 or 3 psi. The crush resistance in the fronds may beless than about 2 psi or less than about 1 psi, depending upon thelength of the fronds, structure of the fronds, crush resistance of theadjacent structures, and other factors that may affect the cantileveredtransfer of radial force from the adjacent stent or circumferentiallink.

Radial strength or crush resistance as used herein, may be determined inpsi by constructing a radial strength test fixture. In general, theradial strength test fixture comprises a pressured chamber, adapted toallow the insertion of a flexible tube which can be sealed at each endto the walls of the chamber such that the exterior wall of the tubing isexposed to the pressure generated in the chamber while the central lumenof the tube is exposed to ambient atmospheric pressure. Any of a varietyof thin walled flexible tubing may be utilized, such as a thin walledlatex tubing, such that the inside diameter of the latex tubing may beapproximately 10% less than the nominal expanded diameter of the stent.The stent is expanded within the tubing, such as by inflating anassociated dilation balloon to its rated burst pressure or otherpressure sufficient to expand the stent to its intended implanteddiameter. The balloon may be deflated and the balloon catheterwithdrawn. The tubing is mounted in the pressure chamber as describedabove. Air or other inflation media may be pumped into the pressurechamber to slowly increase the pressure within the chamber (for exampleat a rate of about 1 psi per second). Once any portion of the centrallumen through the prosthesis has been reduced under pressure to lessthan or equal to 50% of its original lumen diameter, the pressure in thechamber is noted and considered to be the radial force or crushresistance of the prosthesis.

The second radially expandable structure (circumferential link) may alsohave a shorter axial length than the first radially expandable structure(stent). For example, in a coronary artery embodiment, the axial lengthof the stent may be at least 300% or 500% or more of the length of thecircumferential link.

The fronds will have a length in the axial direction between the support52 and the circumferential link 120 of generally in excess of about 2.5mm or 3 mm, and in certain embodiments in excess of about 5 mm. At leastsome or all of the fronds may have a length in excess of about 8 mm,and, in one implementation of the invention intended for the coronaryartery, the frond length is in the vicinity of about 9.4 mm.

The circumferential link may also have a smaller strut profile comparedto the strut profile in the support 52. For example, the cross sectionaldimensions of a strut in the support 52 and/or the fronds may be on theorder of about 0.003 inches by about 0.055 inches in an embodimentintended for coronary artery applications. In the same embodiment, thecross sectional dimensions through a strut in the circumferential linkmay be on the order of about 0.001 inches by about 0.003 inches.

The frond length may also be evaluated relative to the main lumendiameter. For example, in the coronary artery environment, diameters inthe range of from about 2 mm to about 5 mm are often encountered. Frondlengths of at least about equal to the main vessel diameter (e.g. atleast about 2 mm or 3 mm or 4 mm or greater) are contemplated. Frondslengths of as much as 2 times or 3 times or 4 times or more of thediameter of the associated main vessel are also contemplated.

Deployment of the bifurcation prosthesis with linked fronds may beunderstood by reference to FIGS. 14A-14E. In FIG. 14A, the side branchguidewire 121 has been positioned in the side branch and the main vesselguidewire 123 has been positioned in the main vessel. The side branchstent is next deployed in the side branch, with the fronds extendingacross the ostium and into the main vessel. The circumferential link 120may either self expand or be balloon expandable to provide a main vesselstent opening. See FIG. 14B.

Referring to FIG. 14C, the side branch wire is retracted from the sidebranch and advanced between the fronds into the main vessel. The mainvessel wire 123 may be retracted at this point in the procedure. Themain vessel stent is then advanced over the wire through the openingformed by the circumferential link, and through a space between adjacentfronds into the desired position.

Referring to FIG. 14D, the main vessel stent is deployed to entrap thefronds against the vessel wall. The circumferential link is additionallytrapped against the vessel wall. Post dilation to open the side wallopening into the branch vessel may optionally be accomplished, byretracting the side branch wire and readvancing it into the side branch.See FIG. 14E.

Based upon the foregoing description, it will be apparent to those ofskill in the art that the prosthesis of the present invention may beimplanted in a variety of alternative manners. For example, the firstsupport structure (described above as a side branch stent) may bepositioned in the main vessel, distally (from the perspective of thedelivery catheter) of the bifurcation with the fronds extendingproximally across the opening to the side branch. The second supportstructure (referred to above as a circumferential link), if present, ispositioned in the main vessel proximally of the side branch opening. Astandard stent may then be positioned such that the distal end of thestent is within the side branch, and a proximal end of the stent iswithin the main vessel, such as within the circumferential link.

Referring now to FIGS. 3A-8, in various embodiments prosthesis/deliverysystem 205 can include a prosthesis with stent 210 and fronds 220 whichare configured to be captured or otherwise radially constrained by thedelivery system during advancement of the stent through the vasculatureor other body lumen. As shown in FIGS. 3A-3B, fronds 220 can beseparated by axial gaps or splits 230 along the length of the frondstructure. Splits 230 can have a variety of widths and in variousembodiments, can have a width between 0.05 to 2 times the width of thefronds, with specific embodiments of no more than about 0.05, 0.25, 0.5,1 and 2 times the width of the fronds. Fronds 220 can be configured tohave sufficient flexibility to be advanced while in a captured modethrough curved and/or tortuous vessels to reach the more distal portionsof the vasculature such as distal portion of the coronary vasculature.This can be achieved through the selection of dimensions and/or materialproperties (e.g. flexural properties) of the fronds. For example, all ora portion of fronds 220 can comprise a resilient metal (e.g., stainlesssteel) or a superelastic material known in the art. Examples of suitablesuperelastic materials include various nickel titanium alloys known inthe art such as Nitinol™.

Any of a variety of modifications or features may be provided on thefronds, to enhance flexibility or rotatability in one or more planes.For example, fronds may be provided with a reduced thickness throughouttheir length, compared to the thickness of the corresponding stent. Thethickness of the frond may be tapered from relatively thicker at thedistal (attachment) end to the proximal free end. Fronds may be providedwith one or more grooves or recesses, or a plurality of wells orapertures, to affect flexibility. The specific configuration of any suchflexibility modifying characteristic can be optimized through routineexperimentation by those of skill in the art in view of the presentdisclosure, taking into account the desired clinical performance.

It is desirable to have the fronds captured and held against thedelivery catheter or otherwise restrained as the stent is advancedthrough the vasculature in order to prevent the fronds from divaricatingor separating from the prosthesis delivery system prosthesis. Capture ofthe fronds and prevention of divarication can be achieved through avariety of means. For example, in various embodiments the capture meanscan be configured to prevent divarication by imparting sufficient hoopstrength to the fronds, or a structure including the fronds, to preventthe fronds from separating and branching from the deployment balloon asthe balloon catheter is advanced through the vasculature includingtortuous vasculature. In theses embodiments, the capture means is alsoconfigured to allow the fronds to have sufficient flexibility to beadvanced through the vasculature as described above.

In various embodiments, fronds 210 can be captured by use of a tubularcuff 250 extending from the proximal end 241 p of delivery balloon 241as is shown in FIGS. 5A-5C. In one embodiment, the cuff is attached tothe catheter at or proximal to the proximal end 241 p of the deliveryballoon. In alternative embodiments, the cuff can be attached to a moreproximal section of the catheter shaft such that there is an exposedsection of catheter shaft between balloon and the cuff attachment pointwith the attachment point selected to facilitate catheter flexibility.Alternatively, the cuff is axially movably carried by the cathetershaft, such as by attachment to a pull wire which extends axially alongthe outside of or through a pull wire lumen within the catheter shaft,or to a tubular sleeve concentrically carried over the catheter shaft.In either approach, the cuff is positionable during translumenalnavigation such that it overlies at least a portion of the fronds 220.

After prosthesis 210 is positioned at the target vascular site, thestent region is deployed using the delivery balloon as described herein.The frond(s) can be released by withdrawal of the restraint. In mostembodiments, the entire catheter assembly including the cuff or otherrestraint, balloon, and catheter shaft are withdrawn proximally to fullyrelease the fronds. In alternative embodiment the cuff can be slidablywithdrawn while maintaining position of the delivery balloon. Thisembodiment permits frond release prior to or after stent deployment.

Release of the fronds by the cuff can be achieved through a variety ofmeans. In one embodiment, cuff 250 can be configured such that theproximal frond tips 220 t, slip out from the cuff when the balloon isdeployed. Alternatively, the cuff may be scored or perforated such thatit breaks at least partially open upon balloon deployment so that itreleases fronds 220. Accordingly, in such embodiments, cuff 250 can haveone or more scored or perforated sections 250 p. In such embodiments,portions of cuff 250 can be configured to break open at a selectableinflation pressure or at a selectable expanded diameter. In oneembodiment, the cuff material can be fabricated from a polymer that itis more plastically deformable in a radial direction than axially. Suchproperties can be achieved by extrusion methods known in the polymerarts so as to stretch the material axially. In use, such materials allowthe cuff to plastically deform in the radial when expanded by thedeployment balloon, and then to stay at least partially deformed whenthe balloon is deflated so as to still cover the fronds. An example ofsuch a material includes extruded Low density Polyethylene (LDPE).Further description of the use of the cuff 250 and other capture meansmay be found in U.S. patent application Ser. No. 10/965,230 which isfully incorporated by reference herein.

Referring now to FIGS. 9A-11B, an exemplary deployment protocol forusing delivery system 5 to deliver a prosthesis (10) having a stentregion (12) and having one or more fronds (16) will be described. Theorder of acts in this protocol is exemplary and other orders and/or actsmay be used. A delivery balloon catheter 30 is advanced within thevasculature to carry prosthesis 10 having and stent region (12) andfronds 16 to an Os O located between a main vessel lumen MVL and abranch vessel lumen BVL in the vasculature, as shown in FIGS. 9A and 9B.Balloon catheter 30 may be introduced over a single guidewire GW whichpasses from the main vessel lumen MVL through the Os O into the branchvessel BVL. Optionally, a second guidewire (not shown) which passes bythe Os O in the main vessel lumen MVL may also be employed. Usually, theprosthesis 10 will include at least one radiopaque marker 20 onprosthesis 10 located near the transition region between the prosthesissection 12 and the fronds 16. In these embodiments, the radiopaquemarker 20 can be aligned with the Os O, typically under fluoroscopicimaging.

Preferably, at least one proximal marker will be provided on theprosthesis at a proximal end of the transition zone, and at least onedistal marker will be provided on the prosthesis at the distal end ofthe transition zone. Two or three or more markers may be provided withinthe transverse plane extending through each of the proximal and distalends of the transition zone. This facilitates fluoroscopic visualizationof the position of the transition zone with respect to the Os.Preferably, the transition zone is at least about 1 mm and may be atleast about 2 mm in axial length, to accommodate different clinicalskill levels and other procedural variations. Typically, the transitionzone will have an axial length of no more than about 4 mm or 5 mm. (forcoronary artery applications).

During advancement, the fronds are radially constrained by aconstraining means 250 c described herein (e.g., a cuff) to preventdivarication of the fronds from the delivery catheter. When the targetlocation is reached at Os O or other selected location, the constrainingmeans 250 c is released by the expansion of balloon 32 or otherconstraint release means described herein (alternatively, theconstraining means can be released prior to balloon expansion). Balloon32 is then further expanded to expand and implant the support region 12within the branch vessel lumen BVL, as shown in FIGS. 10A and 10B.Expansion of the balloon 32 also partially deploys the fronds 16, asshown in FIGS. 10A and 10B, typically extending both circumferentiallyand axially into the main vessel lumen MVL. The fronds 16, however, arenot necessarily fully deployed and may remain at least partially withinthe central region of the main vessel lumen MVL. In another embodiment,the constraining means can be released after balloon expansion.

In another embodiment for stent deployment, after deploying stent 10,the cuff or other constraining means 250 c need not be removed but canremain in position over at least a portion of the fronds so as toconstrain at least the tip of the fronds. See, e.g., FIG. 12A, discussedin additional detail below. Then a main vessel stent 150 is advancedinto the main vessel to at least partially overlap the fronds asdescribed above. This method provides a reduced chance that thefrond-tips will caught in or on the advancing main vessel stent 150because the fronds are still captured under the cuff. After placement ofstent 150 balloon 32 together the 12 stent portion of the side branchprosthesis is deployed by inflation of 30 balloon. Prosthesis deliverysystem including cuff 250 c are removed (by pulling on catheter 30) torelease the fronds which when released, spring outward to surround asubstantial portion of the circumference of the main vessel stent 150and the delivery procedures continues as described herein. This approachis also desirable in that by having the cuff left on over the fronds,the frond-tips are constrained together resulting in more advancement ofthe main vessel stent 150. This in turn can reduce procedure time andincrease the accuracy and success rate in placement of the main vesselstent 150 particularly with severely narrowed, eccentric, or otherwiseirregularly shaped lesions. In various embodiments, cuff 250 c and/orproximal end of balloon 32 can have a selectable amount of taperrelative to the body of the balloon to facilitate advancement of one orboth of the main vessel stent 150 or stent 10 into the target tissuesite when one device has already been positioned. Such embodiments alsofacilitate placement into severely narrowed vessels and/or vessels withirregularly shaped lesions.

Various approaches can be used in order to fully open the fronds 16. Inone embodiment, a second balloon catheter 130 can be introduced over aguidewire GW to position the second balloon 132 within the fronds, asshown in FIGS. 11A and 11B. Optionally, the first catheter 30 could bere-deployed, for example, by partially withdrawing the catheter,repositioning the guidewire GW, and then advancing the deflated firstballoon 32 transversely through the fronds 16 and then re-inflatingballoon 32 to fully open fronds 16. A balloon which has been inflatedand deflated generally does not refold as nicely as an uninflatedballoon and may be difficult to pass through the fronds. It willgenerally be preferable to use a second balloon catheter 130 for fullydeforming fronds 16. When using the second balloon catheter 130, asecond GW will usually be prepositioned in the main vessel lumen MVLpast the Os O, as shown in FIGS. 11A and 11B. Further details of variousprotocols for deploying a prosthesis having a stent region (12) andfronds or anchors, such as prosthesis 10, are described in co-pendingapplication Ser. No. 10/807,643.

In various embodiments for methods of the invention usingprosthesis/delivery system 5, the physician can also make use ofadditional markers 22 and 24 positioned at the proximal and distal endsof the prosthesis 10. In one embodiment, one or more markers 22 arepositioned at the proximal ends of the fronds as is shown in FIGS. 9Aand 9B. In this and related embodiments, the physician can utilize themarkers to ascertain the axial position of the stent as well as thedegree of deployment of the fronds (e.g., whether they are in captured,un-captured or deployed state). For example, in one embodiment of thedeployment protocol, the physician could ascertain proper axialpositioning of the stent by not only aligning the transition marker 20with the Os opening O, but also look at the relative position of endmarkers 22 in the main vessel lumen MVL to establish that the fronds arepositioned far enough into the main vessel, have not been inadvertentlypositioned into another branch vessel/lumen. In this way, markers 20 and22 provide the physician with a more accurate indication of proper stentpositioning in a target location in a bifurcated vessel or lumen.

In another embodiment of a deployment protocol utilizing markers 22, thephysician could determine the constraint state of the fronds (e.g.capture or un-captured), by looking at the position of the markersrelative to balloon 30 and/or the distance between opposing fronds. Inthis way, markers 22 can be used to allow the physician to evaluatewhether the fronds were properly released from the constraining meansprior to their deployment. In a related embodiment the physician coulddetermine the degree of deployment of the fronds by looking at (e.g.,visual estimation or using Quantitative Coronary Angiography (QCA)) thetransverse distance between markers 22 on opposing fronds using one ormedical imaging methods known in the art (e.g., fluoroscopy). If one ormore fronds are not deployed to their proper extent, the physician coulddeploy them further by repositioning (if necessary) and re-expandingballoon catheters 30 or 130.

Referring now to FIG. 12A-12I, an exemplary and embodiment of adeployment protocol using a deployment system 5 having a prosthesis 10with fronds 16 will now be presented. As shown in FIG. 12A, prosthesis10 is positioned at Os opening O with catheter 30 such that the stentsection 12 is positioned substantially in branch vessel BV with thefronds 16 extending into the Os O and in the main vessel lumen MVL. Inthis embodiment a second delivery catheter 130 containing a stent 150has been positioned in the MVL prior to positioning of catheter 30.Alternatively, catheter 130 can be positioned first and the branchvessel catheter 30 subsequently. In embodiments where catheter 130 hasbeen positioned first, the proximal end of catheter 30 including fronds16 can be positioned adjacent a proximal portion of balloon 132 ofcatheter 130 such that portions of captured fronds 16 and stent 150 arepositioned side by side. Such alignment can be facilitated by lining upone or more radio-opaque markers (described herein) on the twocatheters.

Next, as shown in FIGS. 12B-12C, balloon 32 of catheter 30 is expanded.Then as shown in FIGS. 12D-12E, catheter 30 together with cuff 250 c iswithdrawn from the vessel to uncover and release the fronds 16. Whendeployed, the fronds 16 are positioned between the vessel wall and stent150 and substantially surround at least a portion of the circumferenceof the main vessel stent 150C/delivery system (130) as well as makingcontact with a substantial portion of inner wall Wm of main vessel lumenMVL. Preferably as shown in FIG. 12E, the fronds are distributed aroundthe circumference of the Wall Wm. Also as shown in FIG. 12E one of thefronds 16A may bent back by stent 150, but may not be contacting thevessel wall.

Then, as shown in FIGS. 12F-12H, balloon 132 is expanded to expand anddeploy stent 150 after which the balloon is deflated and catheter 130 iswithdrawn. Expansion of stent 150 serves to force and hold fronds 16 upagainst the vessel wall in a circumferential pattern as is shown in FIG.12G. This essentially fixes the fronds in place between expanded stent150 and the vessel wall. As such, the fronds may serve five functions,first, as an anchoring means to hold stent 12 in place in the branchvessel lumen BVL. Second they serve as a mechanical joining means tomechanically join stent 12 to stent 150. Third, to provide stentcoverage to prevent prolapse of tissue into the lumen as well as in thecase of a drug coated stent to deliver agent. Finally, they also provideadditional mechanical prosthesising (hoop strength) to hold open Os ofthe branch vessel. More specifically, the now fixed fronds 16 can beconfigured to serve as longitudinal struts to more evenly distributeexpansion forces over a length of the vessel wall as well as distributecompressive forces over a length of stent 12.

The prosthesis of the present invention, may be utilized in combinationwith either main vessel stents having a substantially uniform wallpattern throughout, or with main vessel stents which are provided with awall pattern adapted to facilitate side branch entry by a guidewire, toenable opening the flow path between the main vessel and the branchvessel. Three examples of suitable customized stent designs areillustrated in FIG. 13A through 13C. In each of these constructions, amain vessel stent 110 contains a side wall 112 which includes one ormore windows or ports 114. Upon radial expansion of the stent 110, theport 114 facilitates crossing of a guide wire into the branch lumenthrough the side wall 112 of the main vessel stent 110. A plurality ofports 114 may be provided along a circumferential band of the mainvessel stent 110, in which instance the rotational orientation of themain vessel stent 110 is unimportant. Alternatively, as illustrated, asingle window or port 114 may be provided on the side wall 112. In thisinstance, the deployment catheter and radiopaque markers should beconfigured to permit visualization of the rotational orientation of themain vessel stent 110, such that the port 114 may be aligned with thebranch vessel.

In general, the port 114 comprises a window or potential window throughthe side wall which, when the main vessel stent 110 is expanded, willprovide a larger window than the average window size throughout the restof the stent 110. This is accomplished, for example, in FIG. 13A, byproviding a first strut 116 and a second strut 118 which have a longeraxial distance between interconnection than other struts in the stent110. In addition, struts 116 and 118 are contoured to provide a firstand second concavity facing each other, to provide the port 114.

Referring to FIG. 13B, the first strut 116 and second strut 118 extendsubstantially in parallel with the longitudinal axis of the stent 110.The length of the struts 116 and 118 is at least 2 times, and, asillustrated, is approximately 3 times the length of other struts in thestent. Referring to FIG. 13C, the first and second struts 116 and 118are provided with facing concavities as in FIG. 13A, but which arecompressed in an axial direction. Each of the foregoing configurations,upon expansion of the main vessel stent 110, provide an opening throughwhich crossing of a guidewire may be enhanced. The prosthesis of thepresent invention may be provided in kits, which include a prosthesismounted on a balloon catheter as well as a corresponding main vesselstent mounted on a balloon catheter, wherein the particular prosthesisand main vessel stent are configured to provide a working bifurcationlesion treatment system for a particular patient. Alternatively,prostheses in accordance with the present invention may be combined withseparately packaged main vessel stents from the same or other supplier,as will be apparent to those of skill in the art.

FIG. 13D is an image of a main vessel stent having a side opening,deployed such that the side opening is aligned with the branch vessellumen.

Although the present invention has been described primarily in thecontext of a prosthesis adapted for positioning across the Os between abranch vessel and a main vessel prior to the introduction of the mainvessel stent, in certain applications it may be desirable to introducethe main vessel stent first. Alternatively, where the prosthesis of thepresent invention is used provisionally, the main vessel stent may havealready been positioned at the treatment site. The main vessel stent mayinclude a side branch opening, or a side branch opening may be formed byadvancing a balloon catheter through the wall of the stent in thevicinity of the branch vessel. Thereafter, the prosthesis of the presentinvention may be advanced into the main vessel stent, though the sidewall opening, and into the branch vessel, with the circumferential linkpositioned within the interior of the main vessel stent. In many of theembodiments disclosed herein, the circumferential link will expand to adiameter which is approximately equal to the expanded diameter of thebranch vessel support. Thus, upon initial deployment of the prosthesis,the circumferential link may be expanded to a diameter which is lessthan the adjacent diameter of the main vessel. If the prosthesis of thepresent invention is positioned within a previously positioned mainvessel stent, it may therefore be desirable to include a post dilatationstep to expand the circumferential link up to the inside diameter of themain vessel stent and also to deform the fronds outwardly androtationally to conform to the interior surface of the main vesselstent.

While the above is a complete description of the preferred embodimentsof the invention, various alternatives, modifications, and equivalentsmay be used. Also, elements or steps from one embodiment can be readilyrecombined with one or more elements or steps from other embodiments.Therefore, the above description should not be taken as limiting thescope of the invention which is defined by the appended claims.

1. A method for treating a bifurcation between a main lumen and a branchlumen, comprising the steps of: providing a radially expandablescaffold, having a proximal end, a distal end, a support structure onthe distal end, at least two fronds extending proximally from theproximal end of the support structure and axially between the supportstructure and a circumferential link attached to the fronds and spacedfrom the proximal end of the support structure by the fronds, thecircumferential link connected to the proximal ends of at least two ofthe fronds; transluminally navigating the scaffold to a treatment site;and deploying the scaffold at the site such that a distal end of thesupport structure is in the branch lumen and the circumferential link isin the main lumen upstream from the bifurcation.
 2. A method as in claim1, further comprising the step of positioning an inflatable balloon inthe main lumen, and deforming the circumferential link such that itconforms to at least a portion of the wall of the main lumen.
 3. Amethod as in claim 2, further comprising the step of deploying a stentin the main lumen.
 4. The method of claim 1, wherein the at least twofronds are attached to the proximal end of the support structure.
 5. Themethod of claim 1, wherein after deploying the scaffold, the supportstructure is completely in the branch lumen.
 6. The method of claim 1,wherein the circumferential link is connected to the proximal ends ofall of the fronds.
 7. A method of supporting a vessel wall in thevicinity of an ostium between a main vessel and a branch vessel,comprising the steps of: positioning first and second fronds across theostium, each of the fronds having a first end on a first, branch vesselside of the ostium and a second end on a second, main vessel side of theostium, the second end of each of the fronds being coupled with astructure that extends circumferentially around the main vessel, thefronds defining an elongate opening therebetween through which a secondstent can be delivered in the main vessel; supporting the first ends ofthe fronds against the vessel wall on the first, branch vessel side ofthe ostium; and linking the second ends of the fronds with thecircumferentially extending structure on the second, main vessel side ofthe ostium, such that a circumferential distance is maintained betweenthe second ends of the fronds.
 8. A method of supporting a vessel wallas in claim 7, wherein the supporting the first ends step comprisesexpanding a first expandable support structure against the vessel wall.9. A method of supporting a vessel wall as in claim 8, wherein the firstexpandable support structure is attached to the first ends of thefronds.
 10. A method of supporting a vessel wall as in claim 8, whereinthe expanding step comprises permitting the first expandable supportstructure to self expand.
 11. A method of supporting a vessel wall as inclaim 8, wherein the expanding step comprises forcibly expanding thefirst expandable support structure.
 12. A method of supporting a vesselwall as in claim 7, wherein the linking the second ends step comprisespositioning the second ends of the fronds, and wherein the methodfurther comprises supporting the second ends by expanding a secondexpandable support structure against the vessel wall.
 13. A method ofsupporting a vessel wall as in claim 12, wherein the second expandablesupport structure is attached to the second ends of the fronds.
 14. Amethod of supporting a vessel wall as in claim 12, wherein the expandingstep comprises expanding the second support structure such that thesecond ends of the fronds are entrapped between the second supportstructure and the vessel wall.
 15. A method of supporting a vessel wallas in claim 7, wherein the fronds extend helically about a longitudinalaxis.
 16. A method of supporting a vessel wall as in claim 7, comprisingthe step of positioning at least two fronds across the ostium.
 17. Amethod of supporting a vessel wall as in claim 7, comprising the step ofpositioning at least four fronds across the ostium.